Wind turbines are increasingly gaining importance as renewable sources of energy generation, and wind turbine technology has increasingly been applied to large-scale power generation applications. Maximizing energy output while minimizing loads of the wind turbines in varied wind conditions is a challenge that exists in harnessing wind energy.
Typically, a wind turbine includes at least one rotor mounted on a housing or nacelle which is positioned on top of a truss or a tubular tower. Certain wind turbines, designed to provide electrical power to utility grids, include large rotors with diameters extending 80 or more meters. Each of these rotors includes one or more blades. The rotor blades transform the wind energy into rotational energy which drives a generator operationally coupled to the rotor. The generator may be coupled to the rotor either directly or via a gearbox. The gearbox is used for stepping up the inherently low rotational speed of the rotor so that the generator may efficiently convert the rotational energy into electrical power.
Under certain conditions such as an increase in wind speed or a failure of wind turbine components, the rotor of a wind turbine may rotate faster than under normal conditions. If unchecked, the rotor could continue to accelerate until internal forces and resonances cause instability—a phenomenon known as over speeding. To avoid over speeding, modern wind turbines have mechanisms, such as pitch angle controls, for controlling rotor speeds. Furthermore, at least some known wind turbines also include braking systems to satisfy safety requirements. For example, some known wind turbines may include a disk brake to facilitate stopping the wind turbine rotor against full wind torque and/or stored energy sources such as hydraulic accumulators or capacitors to enable braking during power failure.
However, under certain circumstances, there may be a loss of counter torque from the generator for controlling the rotor speed. In other circumstances, there may be a failure during feathering of one or more of the rotor blades. Under such circumstances, the wind turbine may be subjected to over-speeding unless aggressive braking techniques are employed. Aggressive braking techniques may cause mechanical loading of the wind turbine.
Therefore, there is a need for an enhanced method and system for avoiding over speeding of wind turbines.